Touch sensor devices are devices that detect coordinates of a position pointed using a pointer, such as a fingertip and a pen, or occurrence of a pointing operation. Usually, touch sensor devices are used in combination with surface display devices, such as a liquid crystal display (hereafter referred to as “LCD”) and an organic electro-luminescence display (hereafter referred to as “organic EL display”).
User-friendly man-machine interface can be achieved by inputting an output of a touch sensor device to a computer, and controlling the display content in the display unit or controlling instruments by the computer. Touch sensor devices are widely used in everyday life now, such as in a game machine, a personal digital assistant, a ticket vending machine, an ATM (automated teller machine), and a car navigation device. In addition, as performance of computers have become higher and network connection environment has become popular, services provided by electronic devices have diversified. Accordingly, there is an increasing demand for a display unit having a touch sensor device.
Examples of known techniques for touch sensor devices include capacitive sensing type, resistance film type, optical type, ultrasonic type, and electromagnetic induction type. Among such touch sensor devices, a touch sensor device of capacitive sensing type detects a touch of a pointer through a thin material, for example, a thin glass or plastic. Thus, it is not necessary to push the device strongly upon the touch, and thus touch sensor devices of capacitive sensing type are excellent in durability against repeated inputs. By having such a feature, touch sensor devices of capacitive sensing type are widely used in many application fields where durability is needed, such as in industrial use products and white goods (large household appliances).
Such touch sensor devices of capacitive sensing type are classified into projected capacitive type and surface capacitive type.
A projected capacitive type is a type that forms X-Y transparent electrodes in matrix form. X transparent electrodes and Y transparent electrodes are formed with, for example, a glass or insulator layer put between them. When a pointer approaches the X-Y transparent electrodes, the electrostatic capacity between the electrodes increases. A controller detects the change in the electrostatic capacity of X-Y lines, and thus the position of the touching pointer is detected. Since transparent electrode groups that are arranged in parallel to each other are electrically isolated, it is possible to support a multi-touch operation which requires that a plurality of input points being detected simultaneously. By touching the screen with a plurality of fingers simultaneously, it is possible to rotate the target and adjust the resolution of displaying images, for example. For example, Japanese Translation of PCT International Application (JP-A) No. H09-511086 discloses such a technique of projected capacitive type.
Meanwhile, a touch sensor device of surface capacitive type includes: a transparent insulation substrate; a transparent conductive layer uniformly formed on a surface of the transparent insulation substrate; and a thin insulating layer formed on the transparent conductive layer. When driving a touch sensor device of surface capacitive type, AC voltage is applied from detection electrodes formed at four corners of the transparent conductive layer. Upon a user touching the surface of the touch sensor device with a pointer, micro-current flows into the pointer via electrostatic capacity formed by the transparent conductive layer and the pointer. The micro-current flows from each of the detection electrodes at four corners to the point touched by the pointer. The controller detects each of the current values of the micro-currents from the detection electrodes. As the pointer comes closer to one of the detection electrodes, the corresponding electric current increases. Accordingly, the coordinates of the touch position are calculated by using a lack of balance among the four electric currents. For example, Japanese Examined Patent Publication (JP-B) H01-019176 discloses a technique related to such a touch sensor device of surface capacitive type.
The touch sensor device of surface capacitive type represented by JP-B No. H01-019176 has a simple structure of only a transparent conductive film having a uniform touch sensor portion, and detection electrodes formed at four corners of the touch sensor portion. In addition, the number of detection electrodes is fixed, specifically, four, for touch sensor devices with various screen sizes, which brings the advantage that a flexible printed circuit board (hereinafter referred to as FPC (flexible printed circuit)) and a controller can be used universally (commonly) for those touch sensor devices. Accordingly, the touch sensor device of surface capacitance type has an economical structure.
Japanese Translation of PCT International Application (JP-A) No. 2005-505065 discloses an attempt to support multi-touch operations in a touch sensor device that supports only single-touch operations. In JP-A No. 2005-505065, it is determined whether each operation is touching the sensor or moving away from the sensor on the basis of characteristics of time variation of signals. When a single touch and a double touch in which two touches overlap in time have been conducted in order, the coordinates of the second touch position are calculated and reported by subtracting signal data obtained on the single touch (the first touch) that is a touch conducted before the second touch from signal data obtained on the double touch. When a double touch and a single touch have been conducted in order, the coordinates of the position of an unreported single touch, that is, the first touch position, is calculated and reported by subtracting signal data of the second touch, which is a single touch, from signal data obtained on the previous double touch. This technique disclosed in JP-A No. 2005-505065 utilizes that there is a time difference between the time when the first touch is detected and the time when the second touch is detected.
Japanese Unexamined Patent Application Publication (JP-A) No. 2010-157029 describes about a problem that electrostatic capacitive coupling of a user's palm and a surface resistive object affects the inputted coordinates such that the coordinates are shifted from a position actually pointed by a user's finger. In the technology of JP-A No. 2010-157029, it is determined whether the number of touched or approached locations in a coordinate input area is one or two, where the locations are the points which have been touched or approached by an electrical conductor, such as a user's finger. In the technology, a resistance peripheral electrode is formed on the periphery of surface resistance. Then, the number of touched or approached locations is determined as one when a numerical value calculated using the detected current values is smaller than a predetermined value, and two when it is larger than the predetermined value. When the number is determined as two, this means that the user's palm has excessively approaches toward the touch panel. In this case, the touch of the finger is invalidated, and then, the user is prompted to touch again.
The following analysis is given from the viewpoint of the present invention.
The touch sensor device of projected capacitive type represented by JP-A No. H09-511086 has a multi-touch function. However, in order to detect the position coordinates of a pointer correctly, it is necessary to make the pitch of transparent electrodes arranged in parallel smaller than a certain distance. Accordingly, as the screen size increases, the number of transparent electrodes increases. It increases the number of wires to be extending between the transparent electrodes and the controller in the circumference of the touch panel, and the number of terminals of, for example, a FPC. Therefore, the manufacturing cost increases. In addition, an increase of the number of peripheral lines brings a problem of a frame of the touch panel being large.
In a touch sensor device of surface capacitive type represented by JP-B No. H01-019176, it is difficult to detect coordinates of individual touches correctly upon multiple touches by plural pointers. This is because, since electric currents created due to the individual touches join in a uniformly-formed transparent conductive film, the amount of the electric current detected by the controller is the total value of electric currents created due to plural touches, and thus the amount of an electric current corresponding to each of the touches to be used for coordinate detection is not clear. Accordingly, it can be said that a touch panel of surface capacitive type represented by JP-B No. H01-019176 is a touch panel that supports only single touch operations.
In a touch sensor device of surface capacitive type in JP-A No. 2005-505065, although there is a description that two point touches are sequentially recognized using time difference, simultaneous touches cannot be recognized. The reason for this will be described using an example of a pinch gesture operation, which is an operation of conducting a touch with two fingers and then moving the fingers close to each other or apart from one other and is called “pinch-in” and “pinch-out”. During a pinch gesture, two fingers move simultaneously, that is, a time zone when the signal created due to the touch of one finger changes overlaps with a tome zone when the signal created due to the touch of another finger changes. Accordingly, even if the signal is deducted using the time difference, the signals corresponding to respective touches cannot be separated and thus each individual signal is unknown. That is, this technique is provided on the assumptions that a detected operation is any one of an operation that one of two fingers is completely stopped, and an operation of time-shifted touches that one of two touches occurs first and then overlaps with the other touch occurring later or one of two touches occurring together ends and then the other touch remains. Such an assumption limits user's operations and makes user's operations awkward and slow, which is a problem.
JP-A No. 2010-157029 discloses a technology to detect an approach of a user's palm by detecting the bonding number of the electrostatic capacity with the surface resistance and its effect that a one-location touch and a two-location touch can be discriminated from each other. However, the technology can identify a two-location touch, but just determines coordinates of one point and hardly determines coordinates of each of two touch locations separately. In addition, JP-A No. 2010-157029 just discloses a function of, if a two-location touch has been identified, invalidating the touch or assigning the touch to a double click function. Further, since the unit of the value calculated by Mathematical Expression 2 described in JP-A No. 2010-157029 is that of electric current, it is difficult to detect a motion of two fingers because of an influence of the individual difference of the impedance caused due to the touch and an influence of dispersion of the touch areas. In addition, since it is necessary to form resistance peripheral electrode in the circumference of a surface resistance, the manufacturing cost for forming the resistance peripheral electrode occurs. The present invention seeks to solve the problems.